In the safety footwear industry the need to protect the foot within footwear from pointed and sharp objects which might penetrate through the sole and cause undesired and dangerous wounds to the user is known.
Various technical solutions have been developed with a view to solving this problem. The first of these known solutions provides for embedding a sheet of metal of suitable constant thickness in the sole. This solution does however have some disadvantages, among them the fact that this sheet imparts a constant degree of rigidity along the entire surface of the sole, increasing its overall weight and reducing the thermal insulation properties of the sole, apart from the fact that a sole with a sheet of metal is unsuitable for use in environments subject to the action of a metal detector.
Not only this, but the rigidity imparted over the entire length of the sole by the metal sheet gives rise to substantial discomfort during normal walking, particularly when walking on steps, or, to an even greater extent, on the rungs of a ladder, where the supporting surface area is restricted. This also indirectly results in less safe support for the footwear. It must be pointed out that insoles of the type mentioned here are incorporated into safety footwear normally used by persons who are very frequently called upon to use ladders with rungs, such as firemen.
A second solution which has become available as a result of continuous development in the field of polymer materials provides for the use of fabric-based insoles with enhanced properties of resistance to penetration and cutting, which may be suitably attached to the inside of the sole, for example by adhesive bonding or through the application of a separate assembly insole. Typically these insoles, which are also of constant thickness, are manufactured by superimposing a plurality of layers of fabric based on aramid fibres, which are available on the market, for example, under the trade name Kevlar®. Again the use of these insoles nevertheless gives rise to some disadvantages, including the high supply cost of the starting materials and the constant flexibility along the entire length of the insole which does not enable the insole to perform any structural function in the sole.